Stabilized power supply using delta sigma modulator

ABSTRACT

A switching signal generator for a switching power supply employing a DC-DC modulator has an adder, an integrator and a quantizer. A gate driver circuit is provided upstream of a power switch element and receives a quantizer output. By feeding back a gate driver circuit output to the adder of the ΔΣ-modulator, a large phase margin is obtained at a high-frequency switching. The switching signal generator for the ΔΣ-modulation type switching power supply has an improved direct-current transmission linearity characteristic relative to direct-current input, and that is stably controllable and of high efficiency. Furthermore, a DC-DC converter has an adder, an integrator and a quantizer, the integrator having a mechanism for adjusting its gain. The gain-adjusting mechanism receives a signal from a current flowing internally of the DC-DC converter, a voltage internally of the converter, or a converter output voltage to control gain of the integrator so that the amplitude of output voltage of the integrator is not saturated and a comparator is capable of high-speed operation, a ΔΣ-modulation type DC-DC converter is provided that is unlikely to undergo oscillation especially at a high sampling frequency, and that produces a stable output voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a DC stabilized power supply, and moreparticularly to a switching signal generator for use in a switchingpower supply employing a ΔΣ-modulator, in which a switching signal for apower switch element is fed back from a gate driver circuit output tothe modulator, and to a DC-DC converter utilizing ΔΣ-modulation in whichthe gain of an integrator inside a ΔΣ-modulator can be adjusted inaccordance with output of the DC-DC converter.

2. Description of the Related Art

Description will first be made in connection with the switching signalgenerator for the switching power supply.

A conventional PWM (pulse-width modulation) switching signal generatormodulates an input signal by varying its pulse width. In other words, asshown in the block diagram of a PWM switching signal generator in FIG.5, a PWM oscillator 18 generates a gate signal from an input signal 1,which gate signal is amplified by a gate driver circuit 6 to drive apower switch element 7. In the PWM system, the distortion produced atthe gate driver circuit 6 has been unable to be corrected.

A block diagram of a conventional PWM switching signal generator appliedto a step-down chopper is shown in FIG. 6. The voltage applied to a loadand a reference voltage 17 are compared, and its result is inputted intoa PWM oscillator 18 so that a power switch element 7 is controlled bythe output of the PWM oscillator 18. In this generator, however, becausethere is provided no direct feedback path from the gate driver circuit6, the distortion generated at the gate driver circuit 6 has beenimpossible to correct.

Another conventional switching signal generator has been known in which,as shown in FIG. 7, a ΔΣ-modulator 5 is used to output a gate drivesignal to and drive a power switch element 7. In the ΔΣ-modulator 5, aninput signal is integrated by an integrator 3 instead of using the PWMoscillator and quantized to provide a one-bit output signal. With thisgenerator, however, because the feedback is performed upstream of a gatedriver, the distortion produced at the gate driver circuit 6 may not becorrected.

A block diagram of a conventional ΔΣ switching signal generator appliedto a step-down chopper is shown in FIG. 8. The voltage applied to a loadand a reference voltage 17 are compared, and its result is inputted intoa ΔΣ-modulator 5 so that a power switch element 7 is controlled by theoutput of the ΔΣ-modulator 5. In this generator, however, because thereis provided no direct feedback path from the gate driver circuit 6, thedistortion generated at the gate driver circuit 6 has been impossible tocorrect.

As a result, because distortion has not been removed from the gatedriver circuit 6 which directly drives the power switch element 7, thelinearity of the ΔΣ-modulator has been impaired.

Due to the distortion produced at the gate driver circuit both in theconventional PWM system and ΔΣ system, there is caused an error between,in the PWM system, the output signal of the PWM oscillator and the gatedriver output signal and, in the ΔΣ system, between the output signal ofthe ΔΣ-modulator and the gate driver output signal. Thus, when theseconventional switching signal generators are used for controlling aswitching power supply, especially when operated at a high frequency,there will be obtained only a small phase margin, resulting in unstablecontrol.

Furthermore, the addition of a phase correction circuit, which isnecessary to prevent oscillation, increases the number of parts and thusthe cost. In addition, with these conventional generators, in order foran optimum circuit to be designed, an experiment with an actual circuitused has been conducted in many cases, resulting in stable circuitdesign being made difficult and increasing in development time.

Another method has been known in which the linearity is improved byinputting an analog signal and feeding back the output signal of a powerswitch element, as in a switching amplifier utilizing ΔΣ modulationproposed in Japanese Patent Application Laid-Open Specification No.2000-307359.

FIG. 9 is a block diagram of a conventional ΔΣ-modulation system inwhich the output signal of a power switch element is fed back. Thisconventional method, however, has the following drawbacks when used forcontrolling a switching power supply.

If the output current of a switching power supply is small, there willoccur a discontinuity region in which the current flowing through aninductance located in a power supply circuit becomes discontinuous. Ifin this discontinuity region the current flowing through the inductancebecomes zero, an oscillation is caused by a capacity component and aninductance component inside the power supply circuit.

As shown in FIG. 9, with the method of feeding back the output signal ofa power switch element to a ΔΣ-modulator, the noise caused by thisoscillation is also fed back, thereby considerably increasing the numberof switchings of the ΔΣ-modulation output. Consequently, an increase ismade in the switching loss, and a reduction is made in the power supplyefficiency.

In other words, with a conventional switching signal generator, becausethe distortion produced at the gate driver is difficult to remove, animpaired linearity of direct-current transmission characteristicsresults, which in turn results in a small phase margin, thereby readilygiving rise to oscillation.

With the conventional ΔΣ-modulation-utilizing mthod in which thefeedback path extends from downstream of the power switch element toimprove the linearity, a reduction is made in the power supplyefficiency due to the noise caused by the current discontinuity.

Description will now be made in connection with the DC-DC converterutilizing the ΔΣ-modulation.

ΔΣ-modulation is a modulation system in which an input signal isintegrated, the integrated value is compared with a reference voltage toperform quantization, and its output is fed back to a modulator input.Shown in FIG. 13 is a block diagram of a primary ΔΣ-modulator. By usingthis modulation system, switching of a switching element can beperformed to make a DC-DC converter.

With a conventionally widely-used DC-DC converter employing a pulsewidth modulation system (PWM), the switching frequency is constant,whereas with a DC-DC converter utilizing ΔΣ-modulation, the switchingfrequency varies responsive to a converter output. Thus, the latter hasan advantage that a reduction may be made in the switching loss underlight load, and has attracted attention.

Shown in FIG. 14 is one example of a conventional step-down chopperDC-DC converter utilizing ΔΣ-modulation in which, comparison is madebetween a converter output voltage and a reference voltage toΔΣ-modulate an error-amplified signal voltage of the compared voltagesas an input voltage of the ΔΣ-modulator, switching of a switchingelement is made by the output signal of the modulator, and the switchingoutput is inputted into a smoothing circuit to obtain a constant voltageoutput.

The ΔΣ-modulator has at least one integrator, and shown in FIG. 15 isone example of an integrator employing an operational amplifier. Thegain that represents the gradient of variation of the output voltagerelative to the input voltage of the integrator, is determined, if thefrequency component of the signal inputted into the integrator is withinthe operational amplifier band, only by the value of resistance and thecapacitance value irrespective of the gain of the operational amplifier,and is proportional to the inverse of the product of the resistancevalue and the capacitance value.

Where ΔΣ-modulation is employed in a DC-DC converter, care must be takenso as not to saturate the output of an integrator located inside theΔΣ-modulator, otherwise an accurate modulation will not be achieved,with the result that constant-voltage control of the DC-DC converterbecomes unstable, making it impossible to maintain constant the outputvoltage of the DC-DC converter.

Due to the above, the gain of an integrator has conventionally beendetermined so as not to saturate the integrator output. In other words,the amplitude of an integrator generally becomes great when the outputcurrent of a DC-DC converter is small, and hence, in order for theintegrator not to become saturated at that time, it has been necessaryto set the gain low.

With the above conventional method, the amplitude of the integratorbecomes small when the output current of the DC-DC converter is great.Because the gain is set low so that the integrator output will notbecome saturated when the output current is small, there has arisen aproblem that the amplitude of the integrator output is of small valueless than the order of mV.

The quantizer of a ΔΣ-modulator requires a comparator for comparing theintegrator output with a reference voltage. The difference between thetwo voltages that are compared at the comparator is called an overdrive.If the overdrive is large, the variation of the output voltage of thecomparator becomes rapid, making a high-speed operation possible,whereas in contrast, if the overdrive is small in amount, a high-speedoperation cannot be realized.

The minimum overdrive amount generally required for a comparator tooperate at a high speed is from several tens of mV to 100 mV In order toincrease the overdrive amount and enable the comparator to operate at ahigh speed, it has been necessary to increase the gain of theintegrator.

In the conventional method, however, because, for the purpose ofpreventing saturation of the integrator output, the gain of theintegrator is fixed low in conformity with the time when the amplitudeof the output voltage of the integrator is greatest, the comparator maynot be given a sufficient overdrive when the output current of the DC-DCconverter is great, and thus the amplitude of the output voltage of theintegrator is small, making it impossible for the comparator to operateat a high speed.

The low-speed operation of the comparator causes the feedback of theDC-DC converter to be at a low speed, and there has been a problem that,if switching, especially high-frequency switching of the DC-DC converteris made, it gives rise to oscillation.

In other words, with the conventional method, there has been a trade-offin that, if the gain of the integrator is fixed low so as not tosaturate the integrator output, the DC-DC converter undergoesoscillation, and if the gain of the integrator is fixed high so as notto cause oscillation of the DC-DC converter, the integrator outputbecomes saturated and the output voltage becomes unstable.

Thus, with the conventional method, due to this trade-off, the gain ofthe integrator must be made low to such a degree as not to saturate theintegrator output, and must be made high to such a degree as not tocause oscillation of the converter, resulting in designing difficultyand, in addition, in difficulty in realizing a fast-operating converterwithout causing saturation of the integrator.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the above drawbacks, andaccordingly, it is an object of the present invention to provide aswitching signal generator for use in a switching power supply employinga ΔΣ modulator, which is of high efficiency, provides a large phasemargin, and is stably controllable during switching at a high frequency.

It is another object of the present invention to provide a DC-DCconverter employing a ΔΣ-modulator, which is stably controllable duringswitching at a high frequency and produces a stable output voltagewithout undergoing oscillation even at a high sampling frequency.

In order to attain the above objects, the present invention according toone aspect thereof is characterized in that, in a switching power supplyin which an analog input signal or a multi-bit digital signal isinputted into a ΔΣ-modulator, and the modulated signal is amplified at agate driver circuit to perform switching of a power switch element withthe thus amplified signal, the gate driver output is fed back to theΔΣ-modulator.

The ΔΣ-modulator is constituted by at least one adder, one integrator,and one quantizer. The feedback path extends from the output of the gatedriver circuit connected to a quantizer output to at least one adderinput. The at least one integrator is connected to an adder output andhas at least one output connected to the quantizer.

By providing two or more integrators in series connected to the adderoutput, or by providing two or more integrators in parallel connected tothe adder output, the accuracy of sampling will be enhanced by theformer, and a parallel arrangement of outputs will be obtained, makingit possible to provide a precision or multi-output switching powersupply for a small-sized integrated circuit.

Where a continuous-time signal such as an analog signal is inputted intothe ΔΣ-modulator, an analog adder and an analog integrator are used asthe adder at the input of the modulator and the integrator connected tothe adder output, respectively, and where a discrete-time signal such asa multi-bit digital signal is inputted into the modulator, a digitaladder and a digital integrator may be used.

The quantizer is a quantizer that performs sampling on the discrete-timesignal and is connected to the input of the gate driver circuit thatreceives an output signal of the quantizer and supplies thecurrent/voltage sufficient to drive the power switch element. Such agate driver circuit is needed in case the quantizer output isinsufficient to drive the power switch element and is needed for thefed-back signal to fully show its effect.

The feedback path may include an attenuator that adapts a pulse signalof great amplitude of the gate driver circuit to the level of the inputsignal of the ΔΣ-modulator.

Because the feedback path is provided that extends from the output ofthe gate driver connected to a quantizer output to a modulator input, areduction is made in the distortion produced at the gate driver. Inother words, as compared with the conventional PWM system and theconventional ΔΣ-modulator in which feedback is made from immediatedownstream of the quantizer, the distortion produced at the gate drivermay be directly fed back.

Because direct feedback is made from the output of the gate drivercircuit connected to the quantizer output to the modulator input, asatisfactory linearity of input and output characteristics may beobtained, leading to a large phase margin and unlikeliness ofoscillation.

By direct feedback from the gate driver output, the distortion producedat the gate driver circuit may be directly fed back, and as comparedwith the case where the feedback is made from downstream of the powerswitch element, less noise is produced, and when the switching signalgenerator is applied in a switching power supply, a reduction can bemade in the switching loss.

It is apparent that by making the analog input signal direct-currentvoltage, the output is amplified into a direct-current power, making itpossible for the switching power supply to function as direct-currentswitching power supply. It is also possible to make up a ΔΣ-modulationtype chopper power supply by adding a rectifier smoothing circuitdownstream of the power switch element.

The present invention according to another aspect thereof ischaracterized in that, in a DC-DC converter in which an analog inputsignal or a multi-bit digital signal is inputted into a ΔΣ-modulator toperform switching of a switching element with the thus modulated signal,the gain of an integrator inside the ΔΣ-modulator is adjusted inaccordance with conditions of the converter.

The ΔΣ-modulator is constituted by at least one adder, one integratorand one quantizer, a feedback path is provided to extend from theΔΣ-modulator output to at least one adder input, and the at least oneintegrator is connected to an adder output and has at least one outputconnected to the quantizer.

The quantizer performs sampling on a discrete-time signal and isconnected to the input of a gate driver circuit. The gate driver circuitreceives an output signal of the quantizer and supplies thecurrent/voltage sufficient to drive the power switch element.

The at least one integrator is provided with a gain-adjusting circuit.In other words, a current flowing inside the DC-DC converter, voltageinside the converter, or converter output voltage is detected, and bycontrolling either one or both of the resistance value and thecapacitance value as indicated, for example, in FIG. 15 by the detectedsignal, the gain of the integrator may be adjusted.

Furthermore, it is possible to directly detect the output voltage of theintegrator and, in accordance with the detected signal, adjust the gainof the integrator within the range in which the gain of the integratoris so low as not to saturate the amplitude of the output voltage of theintegrator and is so high as to allow high-speed operation of thecomparator.

Because the gain of the integrator may be adjusted within the range inwhich the output voltage amplitude is not saturated while the comparatorcan operate rapidly, by enhancing the gain at the time when theintegrator amplitude is small, the overdrive given to the comparator maybe increased, and thus a high-speed feedback and a stable constantvoltage control of the converter may be realized.

In contrast, by reducing the gain at the time when the integratoramplitude is great, saturation of the integrator output may beprevented, leading to a stable constant voltage control.

Furthermore, if a variation is made in the gain of the integrator, sucha variation is corrected by the feedback from the ΔΣ-modulator output,and thus the input and output linearity of the modulator will not beimpaired, and the operation of the modulator will be maintained stable.

In other words, according to the another aspect of the presentinvention, a stable DC-DC converter is provided in which, relative tothe operating condition of the DC-DC converter, the gain of theintegrator may be adjusted within the range in which the amplitude ofthe output voltage is not saturated and the comparator can operate at ahigh speed, and which does not undergo oscillation and suffers from fewfluctuations in the output voltage.

The above and other objects and features of the present invention willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a switching signal generator according toone embodiment of the present invention;

FIG. 2 is a direct-current transmission characteristic chart showing acomparison between feedback of a gate driver circuit output according tothe present invention and feedback of a quantizer output according to aconventional method;

FIG. 3 is a block diagram of a ΔΣ switching signal generator of thepresent invention applied to a step-down chopper;

FIG. 4 is a Bode diagram showing a gain and phases according to thepresent invention and the conventional method;

FIG. 5 is a block diagram of a conventional PWM switching signalgenerator;

FIG. 6 is a block diagram of the conventional PWM switching signalgenerator applied to a step-down chopper power supply;

FIG. 7 is a block diagram of a conventional ΔΣ-switching signalgenerator;

FIG. 8 is a block diagram of a conventional ΔΣ-switching signalgenerator applied to a step-down chopper power supply;

FIG. 9 is a block diagram of another conventional ΔΣ-switching signalgenerator;

FIG. 10 is a block diagram of a step-down chopper DC-DC converteraccording to one embodiment of the present invention;

FIG. 11 is a block diagram of a specific example of a DC-DC converteraccording to the present invention;

FIG. 12 is a block diagram of one example of an integrator locatedinside a converter according to the present invention, which integratoris provided with a detector circuit;

FIG. 13 is a block diagram of a conventional primary ΔΣ-modulator;

FIG. 14 is a block diagram of a conventional DC-DC converter; and

FIG. 15 is a block diagram of a conventional integrator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings, in which like parts orcomponents are given like reference numerals and duplicated descriptionsthereof will be omitted.

FIG. 1 is a circuit diagram of one embodiment of the present invention.In this circuit diagram, an input signal 1 is inputted into an adder 2,the output of which is inputted through an integrator 3 into a quantizer4. The output of the quantizer 4 is inputted into a gate driver circuit6, and the output of the gate driver circuit 6 is supplied to a powerswitch element 7. There is provided a path by which the output of thegate driver circuit 6 is fed back through an attenuator 19 to the adder2.

As compared with the conventional method in which the output of thequantizer 4 is fed back to the adder 4, by directly feeding back as inthe present invention the output of the gate driver circuit 6 havingundergone at the gate driver circuit 6 either one or both of voltageamplification and current amplification sufficient to drive the powerswitch element 7, a great distortion reduction is made, leading to animproved linearity of the direct-current transmission characteristic.Shown in FIG. 2 is the direct-current transmission characteristic asreferred to above.

FIG. 3 shows an example in which the present invention is applied to astep-down chopper of a ΔΣ modulation type. The voltage applied to a loadand a reference voltage 17 are compared to amplify a differentialvoltage, and a signal obtained by modulating the differential voltage ata ΔΣ modulator 5 is outputted into the gate driver circuit 6 so that apower switch element 7 is driven with a gate drive signal. A structureis provided for feeding back to the ΔΣ modulator 5.

If for example direct-current voltage is inputted by way of power inputby an analog signal, a power-amplified direct-current voltage may beobtained as the output of the power switch element 7. In other words, itis possible for the switching power supply to be driven in accordancewith the output voltage. The signal after modulation is made binary, andthus construction of an integrated circuit is easy and a small-sizedswitching power supply may be provided.

Thus, by feeding back the output of the gate driver circuit 6 to the ΔΣmodulator 5, which output has a current/voltage capacity sufficient todrive the power switch element 7, a great effect is exerted on the inputsignal and the distortion produced at the gate driver circuit 6 may bereduced, and as shown in FIG. 4, a large phase margin is obtained evenat a high-frequency switching of the power switch element 7, leading toa stable control.

Although FIG. 3 and its corresponding description above especiallyconcerns a step-down chopper, it is apparent that the present inventionis also applicable to a step-up chopper and a polarity reversal chopper.

Reference is now made to FIG. 10, which is a block diagram of astep-down chopper DC-DC converter utilizing ΔΣ-modulation according toone embodiment of the present invention. An output voltage of a detectorcircuit 34 is compared with a reference voltage 39, and an outputvoltage of an input error amplifier 38 resulting from the abovecomparison is inputted into an adder 41 of a ΔΣ-modulator 40 andsubjected to ΔΣ-modulation. An output signal of the ΔΣ-modulator 40 ispassed to a gate driver circuit 47 to make switching of a switchingelement 32, and the switching output is inputted into a rectifiersmoothing circuit 33 to provide a constant voltage output.

The output of the ΔΣ-modulator 40 is fed back through a D/A converter 48to the adder 41, and the integrator 42 is provided with a gain controlcircuit 45 for adjusting its gain. The detector circuit 34 detects DC-DCconverter output, the detected signal is amplified at a control erroramplifier 43, and the amplified signal is inputted into the gain controlcircuit 45 so that the gain of the integrator 42 is adjusted at the gaincontrol circuit 45 in accordance with the signal.

Referring to FIG. 11, which shows a concrete example of the presentinvention, an output voltage of the detector circuit 34 is compared witha reference voltage 39, and an output signal of the control erroramplifier 43 is inputted into a comparator 54. The comparator 54supplies a control signal to a switch element 53 located inside anintegrator 42 including an operational amplifier 52 so that the switchelement 53 is turned off when the converter output current is great andthe switch element 53 is turned on when the converter output current issmall.

Due to the above, the gain of the integrator 42 may be adjusted withinthe range in which the gain is so low as not to saturate the amplitudeof the output voltage of the integrator 42, but so high as to allowhigh-speed operation of the comparator 54.

FIG. 12 is a block diagram of an integrator 42 portion inside aΔΣ-modulator 40 according to the present invention, and shows an examplefor detecting and controlling output inside the integrator. The outputof the integrator 42 is rectified at an absolute value circuit 56, therectified signal is averaged at an averaging circuit 55, and theaveraged signal is compared with a reference voltage 39 at an adjustmenterror amplifier 58 to amplify the compared signal.

By controlling a transistor 57 at the input of the integrator 42 withthe signal amplified at the adjustment error amplifier 58, resistors 36of the integrator 42 may be adjusted, with the result that the gain ofthe integrator is adjusted so that the output voltage amplitude of theintegrator will become constant.

As described hereinbefore, according to the present invention, in theswitching power supply employing a ΔΣ-modulator, by feeding back theoutput of a gate driver circuit to the ΔΣ-modulator, distortion at thegate driver circuit may be reduced to drive the power switch element,leading to a large phase margin and a stable control, especially at ahigh switching frequency, without causing oscillation. In other words, aswitching power supply may be provided that is unlikely to give rise tooscillation even at a high switching frequency, and that supplies anoutput voltage corresponding to an input voltage.

Furthermore, according to the present invention, in the DC-DC converteremploying a ΔΣ-modulator, by adjusting the gain of an integrator withinthe range in which the amplitude of the output voltage of the integratoris not saturated and the comparator is capable of high-speed operation,the integrator output voltage amplitude is optimized, so that a DC-DCconverter is provided that does not give rise to oscillation and gives astable constant voltage output especially at a high sampling frequency.

What is claimed is:
 1. A switching signal generator for switching a power switch element used in a switching power supply, comprising: a ΔΣ-modulator for ΔΣ-modulating an analog signal or a multi-bit digital signal such that switching of a power switch element is made in response to the modulated signal to a one-bit signal; a gate driver circuit for a switching signal for which amplifies the one-bit signal and switches said power switch element; and a feedback path for feeding back output of said gate driver circuit to said ΔΣ-modulator.
 2. A switching signal generator according to claim 1, wherein said ΔΣ-modulator comprises at least one integrator and at least one adder, and wherein an output of said at least one adder is connected to said at least one integrator, and an output of said at least one integrator is connected to a quantizer input.
 3. A switching signal generator according to claim 2, wherein said feedback path extends from an output of said gate driver circuit connected to a quantizer output to an input of said at least one adder.
 4. A switching signal generator according to claim 3, wherein said gate driver circuit receives a quantizer output the one-bit signal and performs thereon either one or both of voltage amplification and current amplification sufficient to drive said power switch element.
 5. A switching signal generator according to claim 3, wherein said feedback path comprises an attenuator for adapting a pulse signal of large amplitude of said gate driver circuit to an input signal level of said ΔΣ-modulator.
 6. A switching signal generator according to claim 1, wherein said gate driver circuit receives a quantizer output the one-bit signal and performs thereon either one or both of voltage amplification and current amplification sufficient to drive said power switch element.
 7. A switching signal generator according to claim 6, wherein said feedback path comprises an attenuator for adapting a pulse signal of large amplitude of said gate driver circuit to an input signal level of said ΔΣ-modulator.
 8. A switching signal generator according to claim 1, wherein said ΔΣ-modulator comprises: an adder which adds the analog signal or the multi-bit digital signal and a feedback signal and outputs an output signal; an integrator which integrates the output signal of said adder and outputs an integrated signal; and a quantizer which quantizes the integrated signal output by the integrator; and said feedback path feedbacks the output of said gate driver circuit to said adder as the feedback signal.
 9. A switching signal generator according to claim 8, wherein said feedback path comprises an attenuator for attenuating pulse signals amplified by said gate driver circuit so as to adapt it to an input signal level of said adder.
 10. A switching signal generator according to claim 1, wherein said feedback path comprises an attenuator for adapting a pulse signal of large amplitude of said gate driver circuit to an input signal level of said ΔΣ-modulator. 